Homing display system and method

ABSTRACT

A relative positioning system enabling a user to return to a starting position or some other point on the user&#39;s path. The system may include an array of accelerometers. The output from the accelerometers may be integrated to quantify movement of the array. The various movements of the array may be reconstructed to determine a net two or three dimensional translation. The current location of the array may be compared to a reference point to derive at trajectory directing the user to the reference point, such as an originating point. The trajectory may be continuously or periodically updated. Applications may include various displays presenting images, numbers, pointers, paths, vectors, or data by digital screens, watch faces, or other devices integrated with or remote from the processor calculating the vector back to the point of origin.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/929,968 filed Aug. 30, 2004 now U.S. Pat. No. 7,487,043.

BACKGROUND

1. The Field of the Invention

This invention relates to relative positioning systems, and moreparticularly to apparatus and methods using accelerometers to quantifychanges in position.

2. The Background Art

Scuba-diving is an exhilarating and dangerous pastime. The developmentof underwater breathing capability (e.g. Self-Contained UnderwaterBreathing Apparatus or SCUBA) has opened up a new world underneath theocean. However, a scuba diver is venturing into an alien world for whichhe is ill suited. In particular, determining relative positionunderwater presents many challenges not present when orienting oneselfon land. Both ocean water and lake water typically contain quantities ofparticulate matter that limit visibility. In addition, water isgenerally impervious to radio waves. Accordingly, visual positioningtechniques and radio frequency based Global Positioning System (GPS) arenot available underwater. Use of magnetic compasses likewise is madeimpossible by the inability to take bearings from reference points dueto low visibility. Relative positioning by compass also requires anindividual to evaluate how far one has traveled and in what direction.However, this approach is made impossible by underwater currents. Adiver carried along by a current will have an inaccurate perception ofhow far he or she has actually traveled.

Determining relative position underwater is extremely critical. A scubadiver in the open ocean must be able to return to the boat or be lost atsea. A diver in a cave must be able to find his or her way out. Time isalso critical, inasmuch as a diver must return to a point of originbefore running out of air.

Accordingly, what is needed is a relative positioning system (RPS)enabling a diver to return to a point of origin without reliance onvisual or other land-oriented guidance mechanisms. Additionally, what isneeded is a system able to track a diver's movements and provide atrajectory pointing to a point of origin.

BRIEF SUMMARY OF THE INVENTION

In view of the foregoing, it is a primary object of the presentinvention to provide a system, method, and apparatus for determiningrelative position underwater. An array of accelerometers fixed withrespect to one another may detect acceleration in sufficient orthogonaldirections to accurately describe the movements of the array when theaccelerations are doubly integrated. In some embodiments, accelerationin longitudinal, transverse, and lateral directions may be detected, aswell as rotational acceleration about axes extending in thelongitudinal, transverse, and lateral directions. The array may bemounted on a wrist-based computer, or be mounted to a computer securedto an article of standard scuba gear.

An electronic device, such as a small computer, may integrate the outputof the accelerometers to transform the output from a representation ofacceleration to a representation of velocity. Velocity integrateslikewise to translation. The integrated output is then interpreted ortransformed to derive a description of the current three dimensionalposition of the array.

A trajectory may be calculated based on a current (present) position andan objective point. The objective point may be automatically chosen tobe the starting point. Alternatively, an objective point may be chosenfrom a series of reference points. A user may instruct the electronicdevice that the current position of the array is to be designated as areference point. A diver may then move to or return to that position bysetting the reference point as the objective point.

An electronic device may have a display capable of graphicallyrepresenting the trajectory to a user. For example, an arrow may bedisplayed pointing the way to an objective point. An image of the entiretrajectory may also give a user a more global view of one'scircumstance. This may be toggled with a presentation of the vector in asuitable display.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects and features of the present inventionwill become more fully apparent from the following description, taken inconjunction with the accompanying drawings. Understanding that thesedrawings depict only typical embodiments in accordance with theinvention and are, therefore, not to be considered limiting of itsscope, the invention will be described with additional specificity anddetail through use of the accompanying drawings in which:

FIG. 1 is a perspective view of a watch-based computer hosting arelative positioning system, in accordance with the invention;

FIG. 2 is a schematic block diagram of one embodiment of a computer inaccordance with the invention;

FIG. 3 is a schematic block diagram of a relative positioning system inaccordance with the invention;

FIG. 4 is a schematic diagram illustrating the operation of a relativepositioning system in accordance with the invention;

FIG. 5 is a schematic diagram illustrating an alternative mode ofoperation of a relative positioning system in accordance with theinvention

FIG. 6 is an illustration of the operation of a switching module inaccordance with the invention;

FIG. 7 is a process flow diagram of a method for determining relativeposition in accordance with the invention;

FIG. 8 is a process flow diagram of a method for determining relativeposition using a switching module in accordance with the invention;

FIG. 9 is a side elevation view of a ski in accordance with theinvention;

FIG. 10 is a top plan view of an embedded accelerometer array inaccordance with the invention;

FIG. 11 is a front elevation view of a mask having a LCD display mountedthereon in accordance with the invention; and

FIG. 12 is a process flow diagram of a method for using an embeddedaccelerometer array in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It will be readily understood that the components of the presentinvention, as generally described and illustrated in the Figures herein,could be arranged and designed in a wide variety of differentconfigurations. Thus, the following more detailed description of theembodiments of systems and methods in accordance with the presentinvention, as represented in FIGS. 1 through 12, is not intended tolimit the scope of the invention, as claimed, but is merelyrepresentative of certain examples of presently contemplated embodimentsin accordance with the invention. The presently described embodimentswill be best understood by reference to the drawings, wherein like partsare designated by like numerals throughout.

Referring to FIG. 1, a relative positioning apparatus 10 for useunderwater or elsewhere may include a computer 12. The computer 12 maybe wrist-mounted or be otherwise packaged to enable the computer 12 tobe remain submerged and independently powered. In some embodiments, thecomputer 12 may be incorporated within a dive computer typically used toinform divers of critical dive parameters. The computer 12 willtypically include an LCD 14, or like display for presenting informationto a user.

An apparatus 10 may track acceleration in the number of degrees offreedom (e.g. directions) necessary to track a diver's movements. Insome instances these directions may include a transverse direction 16 a,a lateral direction 16 b, and a longitudinal direction 16 c. It will benoted that the directions 16 a-16 c are defined with respect to thecomputer 12. Rotational directions 18 a-18 c, may be defined as rotationabout axes parallel to the directions 16 a-16 c, respectively. Thedirections 16 a-16 c may be mutually orthogonal to one another. It willalso be noted that any definition of translational and rotationaldirections may be used provided they are sufficient to uniquely identifythe position and orientation of the computer 12.

Referring to FIG. 2, in some embodiments a computer 12 may include aprocessor 20 for executing instructions, processing inputs, andproducing output data. A memory 22 may connect to the processor 20 tostore executable and operational data. A memory 22 may include volatileRAM 24 as well as long term secondary memory 26, such as flash memory ora hard drive. The computer 12 may include an input device 28 such asbuttons or the like to enable a user to input user defined parameters tothe computer 12. Likewise a display 30 may enable the processor 18 todisplay data to a user. A display 30 may include an LCD 14, or othervideo or audio output devices. A signal processor 32 may be dedicated toprocessing analog signals, performing such functions as filtering ormaking analog-to-digital conversions or vice versa.

Referring to FIG. 3, a computer 12 may execute the modules forming arelative positioning system 31. The modules forming the relativepositioning system 31 may be formed as digital or analog circuits.Alternatively, the modules forming the relative positioning system 31may represent computer executables (i.e. executable data) processed bythe processor 20.

A relative positioning system 31 may include a signal processing module32, an integration module 34, a reconstruction module 36, a storagemodule 38, a trajectory module 40, a reference point management module42, a switching module 44, an input module 46 and an output module 48.The input module 46 may receive user instructions directing theoperation of the system 31. For example, buttons, wireless communicationlinks, or other data input means may be used. Likewise, an output module48 may be a liquid crystal display (an LCD) 14, a wireless communicationlink to an external device, or some other means of outputting data.

An array 50 of accelerometers may be electrically connected to a dataacquisition system or other similar computer 12, supplying informationthereto relating to the accelerations experienced by the array 50. Theoutput of the array 50 may be input to the signal processing module 32.The signal processing module 32 may filter the output of the array 50 toeliminate noise and otherwise condition the output to compensate forunwanted components of the output signal.

An integration module 34 may convert the output of the accelerometersfrom a signal representing acceleration to a signal representingvelocity, displacement, or both. The integration module 32 may performthis function by numerically integrating the conditioned signal. A firstintegration of the signal will yield velocity whereas a secondintegration will yield a displacement.

A reconstruction module 36 may reconstruct a three dimensional pathbased on the integrated signal. An array 50 may output signals measuringacceleration corresponding to the six degrees of freedom necessary todescribe the position and orientation of an object in three dimensionalspace (i.e. lateral, transverse, and longitudinal translation androtation about the lateral, transverse, and longitudinal axes).Accordingly, the integrated signal may be converted by thereconstruction module 36 into a description of the acceleration,velocity, and displacement of the accelerometers in three dimensionalspace as well as the rotations experienced by the accelerometers.

A storage module 38 may store such things as the currentthree-dimensional position and orientation of the array 50, the threedimensional position and orientation of the array 50 at a prior point intime that is significant (e.g. the starting position of the diver or oneor more way points specified by the diver), or other points along thepath followed by the array 50. The storage module 38 may automaticallystore such points or store points as instructed by the user. For examplea diver may instruct the storage module 38 that a specific point (e.g.the current position of the array 50) is to be saved as a way point. Insome embodiments, the storage module 38 may store points based on thelength of the path traveled or the amount of time that has passed (e.g.store a point every twenty feet or every 30 seconds). The length of timepassed and distance traveled may be specified by a user or be eitherfixed or chosen automatically.

Referring to FIG. 4, while still referring to FIG. 3, A trajectorymodule 40 may compute a vector 60 indicating a trajectory of someinterest for a user. It will be noted that although FIGS. 4 and 5illustrate a two dimensional path, the trajectory may also represent athree dimensional vector. The trajectory module 40 may evaluate thecurrent position 62 a of the array 50 and a starting point 64 stored inthe storage module 38. The trajectory module 40 may calculate acorresponding vector 60 pointing from the current position 62 a of thearray 50 to the starting point 64 or another selected point ofsignificance. As a user moves from a point 62 a to a point 62 b or 62 c,the trajectory module 40 may update the vector 60 to point from thepoint 62 b, 62 c to the starting point 64 as the user moves from point62 a to points 62 b and 62 c.

Referring to FIG. 5, while still referring to FIG. 3, Alternatively, auser may specify that the vector 60 to be calculated shall point from acurrent position 62 a-62 e to any of a number of saved way points 66 a,66 b. In some embodiments, the trajectory module 40 may calculate atrajectory from the current position 62 to a point a standardizeddistance from the current position. For example, the trajectory module40 may be programmed to constantly update the trajectory to point to apoint on the reconstructed path 20 feet (or some other distance) fromthe current position. In this manner, the trajectory module 40 may aid auser to substantially retrace a path.

In order to facilitate precise retracing the trajectory module 40 maycalculate a trajectory or a curve fit that approximates a tangent line,polynomial or other reconstructed path calculated at, near, or throughthe points on the path closest to the series of current positions of auser and indicating the direction to be followed to retrace the originalpath. That is, a path may include an original path and a return path. Auser may specify to the computer 12 at some point that he is returning,thus defining subsequent additions to the path as the return path. Whencalculating a tangent or other curve-fit trajectory, the trajectorymodule 40 may use the position on the original path closest to thereturn path. Numerical methods and filtering may provide a shortened,smoothed, or otherwise improved return path.

A reference point management module 42 may enable a user to identifyreference points that are to be stored and select which of storedreference points are to be used by the trajectory module 40. Forexample, a user may press a button, or otherwise provide inputs toinstruct the computer 12, and cause that current position of the array50 to be stored as a reference point. A user may repeatedly store pointsas reference points. When a user wishes to retrace a path the referencepoint management module 42 may present a list of reference points, e.g.reference points 66 a, 66 b, and allow a user to select which points areto be used by the trajectory module 40 to calculate a vector 60, returnpath, or the like.

In some embodiments, the reference point management module 42 mayautomatically select which of the stored reference points 66 a, 66 b isto be used to calculate a vector 60. For example, the reference pointmanagement module 42 may march through the reference points 66 a, 66 b,with the last reference point created used first by the trajectorymodule 40. When a user approaches the location of the last referencepoint, the reference point management module 42 may then select the nextto last reference point to calculate a new trajectory, and so on formultiple stored reference points. For example, when a user comes withina specified distance of reference point 66 a, the reference pointmanagement module 42 may automatically select reference point 66 b foruse in calculating the vector 60. In some embodiments, a reference pointmanagement module 42 may be instructed by a user, pre-programmed, orhard wired to select the reference point 66 a, 66 b, or starting point64 based on proximity. For example at point 62 d, the reference pointmanagement module 42 may calculate that point 62 d is closer toreference point 66 b and therefore select reference point 66 b tocalculate the vector 60.

Referring to FIG. 6, while still referring to FIG. 3, a switching module44 may manage interaction between the system 12 and an independentreference system 70. An independent reference system 70 may include aglobal positioning system (GPS), radio frequency beacon system (e.g.OMNI), or the like. In the illustrated embodiment, cell phone towers 72a and 72 b may be used to determine the position of a cellular phone 74,or like device.

However, radio waves may be unavailable in some circumstances. Forexample, a diver will be unable to receive radio frequency signals underwater. Likewise, a cell phone user who travels outside of the servicecoverage areas 76 a, 76 b of available cell phone towers 72 a, 72 b oris blocked therefrom will not be able to use radio contact to determineposition.

Accordingly, a switching module 44 may detect when an independentreference system 70 is unavailable and prompt the other modules formingthe relative positioning system 31 to function as describe hereinabove.For example, a switching module 44 may detect the weakening ordisappearance of radio signals and begin tracking a user's positionusing the signals from the accelerometer array when the intensity ofradio signals falls below a certain threshold. A switching module 44 maylikewise detect when the signal intensity of an independent referencesystem 70 is above a certain threshold and revert to the use of thesystem 70 or simply re-calibrate distances for correction using thesystem 70.

Referring to FIG. 7, a method 80 for using a relative positioning system31 may include setting 82 a reference point. Setting 82 a referencepoint may include storing sufficient data to define a point in threedimensional space based. Setting 82 a reference point may also includestoring an orientation of the array 50. In some embodiments, a firstreference point may be presumed to be the point at which a relativepositioning system 31 is first engaged or powered on. Accordingly,subsequent tracking of the movements of the array 50 will “set” 82 thereference point as simply the point of origin of the reconstructed path.

A method 80 may include conditioning 84 the output of the array 50.Conditioning 84 may include removing noise and other artifacts from thesignal output by the array 50. Conditioning 84 the output of the array50 may be performed prior to integration of the output and prior toreconstruction of the path. Alternatively, the integrated output or thereconstructed path may be smoothed, filtered, or both. In someembodiments, conditioning 84 may be performed by one or more of theoutput of the array 50, the integrated output, and the integrated path.

A method 80 may include integrating 86 the output. Integrating 86 mayinclude using numerical integration techniques to integrate the outputsignal of the array 50. The integration 86 may be performed using analogelectronics or by converting the output of the array 50 into a digitaldata and performing the integration programmatically or through digitallogic circuits.

A method 80 may include reconstructing 88 a path followed by the array50. Reconstruction may include interpreting the integrated output toreconstruct the path. The integrated output may be interpreted asrotations and displacements, which may be interpreted to reconstruct athree-dimensional path followed by the array. The three dimensional pathmay also include a history of the rotations experienced by the array 50.Again, the path may be smoothed to any desired degree by curve fitting.

A method 80 may include setting 90 an objective point, the objectivepoint may be automatically set to be a starting point or first point ona reconstructed path. Alternatively, a reference point, whether createdby a user or automatically, may be set 90, whether automatically ormanually, to be an objective point.

A method 80 may include calculating 92 a trajectory. Calculating 92 atrajectory may include calculating a vector pointing from the currentlocation of the array 50 to the objective point chosen in step 90. Thevector may be displayed 94 on the LCD 14 of the computer 12, ortransmitted to another device and displayed 94. For example, an arrowpointing to the objective point may be displayed on an LCD of awatch-based computer 12.

Referring to FIG. 8, a method 80 may have various alternativeembodiments. In the embodiment of FIG. 8, the method 80 is used todetermine relative position in regions where independent referencesystems 70 are unavailable. A method 80 may include detecting 102 signalloss. Detecting 102 signal loss may include detecting when reception ofa signal is so poor as to render reliance on the signal improper.Detecting 102 signal loss 102 may include measuring the intensity of thecarrier wave transmitting a signal and comparing the intensity to apredetermined value. Likewise, relative variation in signal intensitymay be used in addition or instead.

The method 100 may include storing 104 the current position of the array50 at, or near, the time when the signal loss is detected 102. In someembodiments, the current position of the array 50 may be constantly andrepeatedly stored on some schedule, such that when the signal loss isdetected 102, one or more accurate locations will be preserved. Storing104 the current position of the array 50 may also include storing theorientation of the array 50. The steps of conditioning 84 the output,integrating 86 the output, and reconstructing 88 a path may be performedas described hereinabove in order to track subsequent movements of thearray 50.

A method 80 may be further modified to include calculating information106 relating to relative position and may include using thereconstructed path and the location stored in step 104 to provideinformation to a user relating to relative position. For example, auser's location with respect to a map of an area may be identified.Displaying 108 relative position information may include displaying to auser the information calculated in step 106. For example, a digitalrepresentation of a map with markings indicating a user's location maybe displayed. This may provide not just a vector instructing whichdirection to move, but perspective and context. Moreover, the vector,destination, path, or all of the above may be displayed schematically orto scale on a compass grid, Cartesian coordinate grid, polar coordinategrid, or the like.

Referring to FIG. 9, a relative positioning system 31 may be used inconjunction with a ski 120, snow board 120, wristwatch, hand helddevice, or other type of recreational equipment, such as a surf board,skate board, bicycle, backpack, or the like. Such an integrated devicewill ensure that the sportsman can always return to a known pointwithout fear of becoming lost. On land or water, a user can backtrack,beeline, or jink around obstacles, yet a relative positioning system 31in accordance with the present invention will always indicate thecorrect direction toward “home” (e.g. a reference point 66 of particularinterest or importance).

Additionally, a relative positioning system 31 may calculate thedistance between a current position 60 and a reference point 66. Summingor integrating in each dimension can provide net distances in two orthree dimensions. Thus, one may always know the direction and distance“home” to a starting point or a destination. A relative positioningsystem 31 may be operative in two or three dimensions and beincorporated into sporting equipment, a wristwatch, hand held device, orthe like. Additionally, a relative positioning system 31 may securedirectly to, or be incorporated as an integral part of, a ski 120, snowboard 120, bicycle, backpack, and the like for all the functionalitydiscussed hereinabove.

Furthermore, when skiing, for example, one's weight distribution on theskis may be critical to correctly execute turns and like maneuvers.Changes in weight distribution may be accompanied by changes in therelative position of points 122 a-122 c along the length of the ski. Forexample, if a skier's weight is shifted forward, the point 122 c mayshift upward. In some instances, torsional flexing of the ski may alsobe reflective of weight distribution or otherwise important to examine auser's technique. Thus, an apparatus 10 in accordance with the inventionmay provide comparisons of minute variations in timing, acceleration,speed, and position for diagnostics and training.

Accordingly, a relative positioning system 31 may be used to monitor themotion of the points 122 a-122 c. Tracking the motion of the points 122a-122 c may enable a user to reconstruct a model of the motion of theski in order to give feedback to skiers regarding their weightdistribution, velocity, turning technique, timing, stance, positioningand the like.

Referring to FIG. 10, the array 50 of accelerometers may include threeor more distinct arrays 130 a-130 c. The arrays 130 a-130 c may detectacceleration in at least one dimension. For example, the arrays 130 aand 130 c may detect acceleration corresponding to transverseacceleration only, inasmuch as upward deflection of the tip and tail ofthe ski may be of interest. An array 130 b may detect acceleration inall six degrees of freedom in order to provide an accurate descriptionof the motion of the skier. In some embodiments, each array 130 a-130 cmay detect motion in multiple directions. For example, arrays 130 a, 130c may also detect rotation in rotational direction 18 c in order totrack torsion of the ski.

Arrays 130 a-130 c may connect to serial wires 132 a-132 c tocommunicate the output of the arrays 130 a-130 c to other devices. Awire 134, or plate may likewise connect the arrays 130 a-130 c toanother device. The wires 132 a-132 c, 134 may be positioned between alower layer 136 and an upper layer 138 of laminate layers forming theski 120. Apertures 140, or an aperture 140, may be formed in the upperlayer 138 to enable access to the wires 132 a-132 c. A computer 12 maysecure to the ski 120 or other recreational member 120 near theapertures 140 and receive the outputs from the arrays 130 a-130 c.

In some embodiments, the LCD 14 of the computer 12 may display datacalculated by the relative positioning system 31 such as velocity,distance traveled, or the like. In some embodiments, the computer 12 maytransmit the output of the arrays 130 a-130 c, or data calculated usingthe arrays 130 a-130 c to an external device using wirelesscommunication transmitters and receivers. In some embodiments, thecomputer 12 may simply store the output, or the result of operationsexecuted on the outputs, in its RAM 24 or secondary memory 26 to beretrieved later. It will be noted that the computer 12 may be positionedon the ski 120 or in some other location. The output of the arrays 130a-130 c may simply be stored or transmitted to a computer 12 located onthe skier's person or elsewhere

Referring to FIG. 11, in some embodiments, the output of calculationsmay be displayed on a mask 142 worn by a user. Using LEDs, LCDs or otherdisplay technology, a user may move a display area of a face mask, or a“heads-up” display on a part of the mask. For example, an LCD 14 may bepositioned on the mask 142. Alternatively, graphical representations ofdata may be projected onto the mask 142 for viewing by the user. In someembodiments, the computer 12 may also secure to the mask 142 and receivethe output of the arrays 130 a-130 c from a wireless transmitter securedto the ski 120 or from wires extending from the ski 120 to the mask 142.

Referring to FIG. 12, a method 80 may be modified as illustrated for usewith a ski 120. For example, the output of the array 50, or of some stepof the processing of the array output, may be transmitted 150 from thearray 50 to another device. For example, the computer 12 may be remotefrom the array. Transmitting 150 the output may be accomplished by meansof wires or wireless transmission.

Context data may be input 152 to a computer to enable interpretation ofthe reconstruction of the path of the array 50. For example, a model ofthe ski to which the array 50 is attached may be input. Critical data154 may be isolated from the reconstructed path. For example, the topspeed or maximum altitude obtained may be determined based on thereconstructed path. In some embodiments, identifying a maximum altitudemay include analyzing which maximum altitude is of significance. Forexample, a skier performing a jump will start at the top of a hill,descend the hill to gather speed, engage a ramp, ascend through the airuntil an apex is reached, and then descend. The starting position of theskier will likely be the absolute maximum, with the apex of the jumpbeing a local maximum. Accordingly, a large parabolic portion of thepath may be isolated to identify the region where the maximum altitudeis to be found. Similarly, curve fitting and filtering may isolatefeatures of interest.

The critical data isolated in step 154 may be displayed in step 156. Forexample, a top speed or maximum altitude may be displayed on the top ofa ski or a display secured to a skier's mask 142. Alternatively, thecritical data identified in step 154 may be stored to be displayed 156at a later time.

In some embodiments, an animation of a rider's, boarder's, or skier'spath may be rendered 158 using the context data of step 152 and thereconstructed path of the array 50. Rendering 158 an animation mayinclude applying translations and rotations to a digital model of a ski,bike, board, or the like. The animation may then be displayed 160 to auser in order to provide feedback to improve technique or performance.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrative,and not restrictive. The scope of the invention is, therefore, indicatedby the appended claims, rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. A homing display method comprising: connecting to a user a portable,self-contained apparatus moving with the user, the apparatus comprisinga processor executing relative positioning software, an array ofaccelerometers operably connected to the processor and detectingacceleration of the user in at least two of transverse, longitudinal,and lateral directions, and a display; positioning the array and user inan environment comprising a fluid moving with respect to the earth;moving the array and user through and within the environment along anindirect path from a starting point, fixed in space with respect to theearth, through a series of locations to a current position; providing,by the array in response to the moving, a first signal to the processor;operating the relative positioning software to receive updates to thefirst signal; calculating, by the processor based exclusively on thefirst signal, a vector pointing directly back from the current positionto the starting point; substantially continually, by the relativepositioning software, altering the vector to reflect the relativeposition of the starting point with respect to the current position ofthe user; providing by the processor to a display a second signalcorresponding to the vector; displaying to the user a sensible signaldirecting the user directly along the vector toward the starting point;and updating substantially continually the sensible signal to pointdirectly toward the starting point with respect to the current positionof the user.
 2. The method of claim 1, wherein the sensible signal is adirector pointing to the starting point and the method furthercomprises: traveling, by the user, in a first direction indicated by thedirector toward the starting point; updating, by the relativepositioning software, the vector; and displaying to the user, on thedisplay, connected to the user, an updated director pointing to thestarting point.
 3. The method of claim 2, wherein the fluid is water andthe display is selected from a liquid crystal display, a video device,an analog device, and an audio device.
 4. The method of claim 3, whereinthe director is selected from a pointer on the liquid crystal display, apointer on the video device, a needle on the analog device, and anaudible signal from the audio device, designating a direction.
 5. Themethod of claim 3, wherein the processor executes a signal processingmodule filtering at least one of the first and second signals.
 6. Themethod of claim 5, further comprising converting, by the signalprocessing module at least one of the first and second signals.
 7. Themethod of claim 6, wherein converting includes at least one ofanalog-to-digital conversion and digital-to-analog conversion.
 8. Themethod of claim 1, wherein the display is selected from the groupconsisting of a video display, LCD display, audio sound generator, aheads-up display, a projector projecting onto a face mask, a watch face,watch hands, and a combination of one or more thereof.
 9. The method ofclaim 8, wherein the sensible signal is selected from the groupconsisting of a graphic, a digital pixel image, a pointer, an arrow, apicture of a trajectory of the user, toggled alternative views of anarrow pointing a future trajectory toward the starting point and animage of a past trajectory from the starting point, a needle pointing adirection, a needle pointing a direction on a marked watch face,alphanumeric data, a pointer on an image of the points of a compass, apointer on a Cartesian grid, a pointer on a polar grid, alphanumericdata representing at least one of position, direction, velocity, anddistance, graphical data representing at least one of position,direction, velocity, and distance, a map, a projection onto a mask ofthe user, an animation of the path of the user, and a combinationthereof.
 10. A method of guiding a user back toward an origin of a trip,the method comprising: providing an apparatus, self contained andconnected to the user, the apparatus comprising a processor and an arrayof accelerometers, the array of accelerometers detecting acceleration ofthe apparatus in at least two of transverse, longitudinal, and lateraldirections; positioning the array of accelerometers and user in a fluidmoving with respect to the earth; moving, during the trip, the entireapparatus with the user through and within the fluid along a path fromthe origin to a current position; providing, by the array ofaccelerometers, data and updates to the data to the processor;calculating, by the processor, based exclusively on the data and updatesto the data, a future trajectory of the user, the future trajectorypointing directly back from the current position to the origin;substantially continually, by the processor, altering the futuretrajectory to reflect the relative position of the origin with respectto the current position of the user; displaying to the user a sensiblesignal communicating the direction of the future trajectory; andupdating substantially continually the sensible signal to point directlytoward the origin with respect to the current position of the user. 11.The method of claim 10, further comprising; traveling by the user towardthe origin a first distance; calculating by the processor a new futuretrajectory pointing directly back to the origin; traveling by the usertoward the origin a second distance; and displaying to the user anupdated trajectory pointing directly back to the origin.
 12. The methodof claim 10, wherein the apparatus further comprises a displayconfigured to present to the user an image, and wherein displayingfurther comprises displaying an image selected from the group consistingof a graphic, a picture rendered on digital pixels, a pointer, an arrow,an image of the path from the origin to the current position, twoalternatively toggled images showing an arrow pointing back to theorigin and the entire path of the trip at least up to the currentposition, a map of the entire path of the trip.
 13. The method of claim10, wherein the apparatus further comprises a display selected from thegroup consisting of an LCD, a video screen, and a static digitalmonochrome display.
 14. The method of claim 10, wherein the apparatusfurther comprises a display presenting a watch face.
 15. The method ofclaim 10, wherein the apparatus further comprises a display comprisingan audio sound generator presenting sounds intelligible to the user anddirecting the user back to the origin.
 16. The method of claim 10,wherein the path reflects locations of the user along the trip from theorigin to the current position and wherein the apparatus furthercomprises a display and displaying further comprises the displaypresenting to the user at least one of a context of the path; aperspective of the path; a map; and a schematic image of at least twoof: the path, the origin, the current position, and a vector directingthe user directly to the origin.
 17. The method of claim 16, wherein themap is marked to indicate at least one of the origin, the path, thecurrent position, a pointer directed to the origin, and a vectorrepresenting distance and direction from the current position to theorigin.
 18. The method of claim 10, wherein displaying comprisespresenting to the user at least one of: the standard points of acompass; a Cartesian coordinate grid; a polar coordinate grid; a digitalimage of the origin and the current position; a heads-up display; an LCDon a mask of the user; projections of an image onto a mask of the user;an animation of the path; a reconstructed image of the path showing thepath close to the origin; data sensible directly by the user anddirecting the user directly to the origin; and data representingvelocity and distance of the user from the current position toward theorigin.
 19. A method comprising: providing an apparatus, self-contained,connected to a user, and comprising a processor, display, and an arrayof inertial sensors, all operably connected; positioning the array anduser in a fluid moving with respect to the earth; sending by the arrayto the processor first signals reflecting motion of the user, beginningat an origin; moving by the user away from the origin through and withinthe fluid along a path comprising translations and rotations withrespect to the earth; executing, by the processor, an executablecomprising a relative positioning system calculating substantiallycontinuously a current position of the user based exclusively on thefirst signals; sending to the display from the processor second signalsreflecting a vector pointing directly back to the origin from thecurrent position; substantially continually, by the processor, alteringthe vector to reflect the relative position of the origin with respectto the current position of the user; displaying by the display a thirdsignal sensible to the user and pointing to the origin substantiallyregardless of the current position of the user and changes thereof; andupdating substantially continually the third signal to point directlytoward the origin with respect to the current position of the user.